I doubt anyone would deny that at the moment, the Republican Party takes a harsher view of apostasy than their Democratic counterparts.You know, I think I might be tempted to deny it.
Now, I'll agree in one set of cases: primary elections in inhospitable states or districts. There, I think we can see a real difference; Democrats in GOP-leaning districts generally try to find a candidate who can win even if she won't be a reliable vote in Congress, while Republicans tend to prefer to lose with a purist than to win with a moderate.
At the presidential level, though...well, it's no more likely that Democrats would nominate a pro-life candidate than that Republicans would nominate someone who was pro-choice. If you look at the three leading Democratic candidates in 2008, there was very little room between them on issues, and in fact that's true for the second tier (Richardson, Dodd, Biden) as well. Waldman notes that much of the field in 2004 (and Hillary Clinton in 2008) had supported the Iraq war, but the only candidate to really still support it in 2004, Joe Lieberman, was treated as a crank in his presidential campaign and then promptly defeated in a primary for re-election to the Senate.
Suppose Barack Obama chooses not to run tomorrow. In the ensuing scramble for the Democratic nomination, would any candidate have a chance if she opposed a public option on health care? Card check? Some sort of serious action on climate? No way.
And focusing on small differences, including differences in how the current orthodox views were arrived at, is a normal consequence of primary election battles. Democrats do it too.
There is a difference between the parties right now, at least in my view, but that difference isn't about "view of apostasy" (great phrase, though), at least at the presidential level.
No, the difference between the parties is how well party dogma is aligned with reality. Budget reality: Republicans are required to believe in balancing budgets by cutting taxes. Political reality: while both parties have their share of relatively unpopular issue positions, Republicans have far more of these, are farther from the median voter on them, and have less leeway to downplay unpopular stances. And reality reality: Republicans are required to be skeptical of evolution, to deny climate change, pretend missile defense works, and otherwise ignore real-world evidence.
Moreover, and perhaps less subjectively, I think there's a real difference between the parties in the way that positions on public policy come to be required. I believe, but do not know as a fact, that this has to do with what my brother calls the "movement conservative marketplace." Basically, the argument would be that while normally parties take positions based on a mix of what party-aligned groups demand, where the median voter is, and what party-aligned idealists want, the Republican Party right now is also affected by a large group of consumers eager to shell out money to the harshest, purist, and most extreme version of "conservative" out there -- which means that the producers of such things are constantly trying to differentiate themselves from moderates. This doesn't dictate all GOP policy positions, but call it a fourth element that has little grounding in any of the factors that normally keep a party firmly tied to reality. Especially if we stretch it and consider purist idealism a form of ideological reality, which at least in my opinion is also missing from a lot of GOP policy positions (that is, they are "conservative" in the sense of being aligned with what Rush or Beck says, but not in the sense of being aligned with ideological conservatism.